Here is the tach dash wiring order, by color.
pin#   wire color
1     gray/blue
2     blue/white
3     brown
4     empty
5     red
6     yellow/red
7     violet/black
8     black
9     green
10    blue/red
11    blue
12    empty (yellow on 2.1 engines)
13    blue/black
14    blue/green

Here is the tach dash wiring order, by color and function
pin#   wire color
1     gray/blue         instrument lighting
2     blue/white        hi beam indicator led
3     brown             ground
4     empty
5     red               clock power
6     yellow/red        temp gauge
7     violet/black      fuel gauge
8     black             +12 (for temp,fuel,tach,leds)
9     green             tach from coil, need to add this on pre 85
10    blue/red          turn signal led
11    blue              alternator led
12    empty(yellow 2.1) none (except on 2.1 oil pressure high switch)
13    blue/black        oil pressure
14    blue/green        OXS led (use this for glow plug led on diesels)

Most of these wires are present but in the wrong pins on pre 85 dashes.
Move the wires to the right spot to use the 85 and later tach clusters.
The unused white/red (old pin 12) wire can be cut down to a couple of
inches and
used in pin 9 where you then attach a green wire that you must run
from the ignition coil where another green wire is already connected.
Diesels use the white/red though so these instruction are not exactly
right for them.

Even non-tach dashes from 86 on have this wiring color and signal order.
On these nothing need be done to add a tach except swap the clusters.

Mark Drillock